| Abstract | Cilj ovog rada bila je priprema grafena redukcijom grafenova oksida fenolnim spojevima iz vegetacijske vode masline kod različitih pH vrijednosti. Provedena je redukcija grafenova oksida (GO) u grafen (rGO) pri pH vrijednostima 7 i 10 na 80°C korištenjem otopine ekstrakta lista masline (ELM) i vegetacijske vode masline (OMW). Vrijeme redukcije u sva tri slučaja iznosilo je pet sati, a dobiveni su produkti rGO(ELM, pH=7), rGO(ELM, pH=10) i rGO(OMW, pH=10). Tijek redukcije praćen je UV/Vis spektrofotometrijom pa je tako dobiveno da apsorbancija u početku raste, što se može objasniti formiranjem rGO čestica koje reflektiraju zračenje. Apsorbancija potom pada, što se može objasniti smanjenjem koncentracije GO, što je ujedno dokaz nastanka rGO. Dobiveni produkti okarakterizirani su metodama cikličke voltametrije, UV/Vis spektrofotometrije i mjerenjem električne provodnosti metodom četiri točke. Cikličkom voltametrijom ispitana su tri različita uzorka rGO. Pri tome je kao strujni kolektor korištena elektroda od staklastog ugljika (GC). Uzorak rGO(ELM, pH=10) pokazuje najbolje kapacitivno ponašanje, dok je najlošije kapacitivno ponašanje dobiveno kod rGO(ELM, pH=7) uzorka. Nakon redukcije u uzorku rGO(OMW, pH=10) zaostali su polifenolni spojevi, a kao posljedica toga došlo je do formiranja anodnih i katodnih strujnih vrhova u cikličkom voltamogramu. Najveća vrijednosti specifičnog kapaciteta od 25,11 F g^-1 zabilježena je kod rGO(OMW, pH=10) uzorka. Specifični kapaciteti povećavaju se smanjenjem mase uzorka koji je nanesen na elektrodu. Usporedbom kapaciteta dobivenih ispitivanjem uzoraka rGO(ELM, pH=10) i rGO(ELM, pH=7) utvrđeno je da se redukcijom pri višem pH dobivaju materijali većih specifičnih kapaciteta. Električna provodnost uzoraka mjerena je metodom četiri točke. Najveća električna provodnost izmjerena je uzorku rGO(OMW, pH=10) i iznosi 15,401 S cm^-1 dok je najmanja vrijednost izmjerena za uzorku rGO(ELM, pH=7) i iznosi 1,206 S cm^-1. |
| Abstract (english) | The main goal of this research was the preparation of graphene by means of chemical reduction with phenolic compounds present in olive vegetation water at various pH values. The reduction of GO has been carried out at pH 7 and 10 and temerature of 80°C using olive leaf extract (ELM) solution and olive mill wastewater (OMW). The duration of the experiment, in all three cases, was five hours, resulting in rGO(ELM, pH=7), rGO(ELM, pH=10) and rGO(OMW, pH=10) products. The course of the reduction was monitored using UV/Vis spectrophotometry where it was discovered that in the begining of the reduction process absorbance increases, which can be explained by the formation of rGO particles that reflect radiation. After that, the absorbance decreases, which could be explained by the decrease in GO concentration, which is also proof that rGO was formed. The obtained products were characterized using cyclic voltametry, UV/Vis spectrophotometry, and four point probe method. Three different samples of rGO have been examined by cyclic voltametry during which a glassy carbon (GC) electrode was used as a current collector. rGO(ELM, pH=10) sample has shown the best capacitive properties, while the poorest have been noticed for rGO(ELM, pH=7) sample. Some residual polyphenolic compounds have been noticed in rGO(OMW, pH=10) sample, as a result, anodic and cathodic current peaks were formed in the cyclic voltammogram. The highest specific capacitance, 25,11 F g^-1, has been registered for rGO(OMW, pH=10) sample. Lowering the mass of samples deposited on the electrode causes an increase in specific capacitance values. By comparing capacitance of rGO(ELM, pH=10) and rGO(ELM, pH=7) samples it has been found that materials obtained by reduction at a higher pH value have better specific capacitance values. Electrical conductivity was measured using four point probe method. The highest electrical conductivity value has been obtained for rGO(OMW, pH=10) sample and amounts to 15,401 S cm^-1 while rGO(ELM, pH=7) sample had the lowest specific capacitance of 1,206 S cm^-1. |
